1. Field of the Invention
The present invention relates to a run-flat tire capable of continuously running even when tire puncture occurs.
2. Description of the Related Art
As shown in Japanese Patent Application Laid-open No. 2002-301914 for example, there is a known run-flat tire provided at its sidewall portion with a side reinforcing rubber layer having high load-supporting ability and having substantially falcate cross section. This run-flat tire can continuously run by about 100 km by suppressing a deflection amount of the sidewall portion when tire puncture occurs.
However, although the tire is a run-flat tire, if a running distance in the blowout state is increased, the sidewall portion is gradually heated due to periodical bending deformation and inside rubber material and cord material are thermally destroyed. If the run-flat tire is further continuously allowed to run, the sidewall portion is heated to about 200° C., the tire completely loses the load-supporting ability and can not run any more. In order to increase the run-flat running distance, it is important to reduce the deflection of the sidewall portion and to suppress the heat.
According to the conventional run-flat tire, a large side reinforcing rubber layer is used to suppress the deflection of the sidewall portion. However, such a tire has great weight and this deteriorates fuel economy. Further, since the rubber thickness of the sidewall portion is increased, heat storing degree is high, and sufficient improving effect can not be obtained.